The leak tightness of an object may be necessary or desired to determine for different reasons. For example, it may be necessary to test the leak tightness of a product in order to guarantee a certain quality of the product, or to test the leak tightness of a product or industrial facilities due to environmental concern. Typical examples of products required to be tested for leakage are parts of refrigeration systems for industrial, commercial, domestic and automotive use as well as liquid and gas carrying parts in the automotive industry, such as for example fuel tanks and aluminium wheels.
Today there are many known systems and methods for performing leak testing of an object. Some of them are based on tracer gas techniques, whereby the presence of a tracer gas is utilized for detecting leaks. The tracer gas, or a gas mixture comprising the tracer gas, is then detected after leak passage by means of a detecting instrument. Examples of commonly utilized tracer gases are helium, hydrogen, refrigerants, sulfur hexafluoride and carbon dioxide.
One tracer gas method for performing leak testing of an object is the so-called sniffing method. In the sniffing method, the test object is pressurized with a tracer gas. Tracer gas leaking out of the object is detected by tracer gas detecting equipment comprising a sniffer probe with a sniffer tip and a tracer gas sensor. The sniffer probe picks up any tracer gas that has leaked out of the test object by means of the sniffer tip and mediates the tracer gas to the tracer gas sensor.
Another tracer gas method for performing leak testing of an object is the so-called spraying method. In the spraying method, the test object is under vacuum and the interior of the test object is connected to a tracer gas detecting equipment comprising a tracer gas sensor. Tracer gas is sprayed onto the test object on the outside thereof by means of a tracer gas spraying device with a spraying tip, i.e. tracer gas is mediated from a tracer gas source by means of the spraying tip onto the outside of the test object. Any tracer gas that enters the test object is then detected by means of the tracer gas detecting equipment.
Both the sniffing method and the spraying method may be applied for local leak detection, i.e. leak detection at a specific leakage testing point. Local leak detection may also be called pin pointing. In local leak detection, the sniffer tip and the spraying tip, respectively, are positioned at a leakage testing point of the object in order to test the leak tightness of that specific leakage testing point. However, in order for the sniffing method and the spraying method, respectively, to be reliable when they are applied for local leak detection, the sniffer tip and the spraying tip, respectively, have to be positioned within a predetermined distance interval from the leakage testing point. In case a sniffer tip or spraying tip, respectively, is not positioned within the correct distance interval from the leakage testing point, the tip might not be able to pick up or spray, respectively, the tracer gas in a correct way. Incorrect test results may then be obtained. The tested objected may then be determined as leak tight in spite of the fact that there is a leak or may be determined as having a smaller leak than it actually has. Thus, the test object may then be determined to be “OK” even though it is not according to the requirements of the test.
The predetermined distance interval depends on the many different factors. For example, it depends on properties of the utilized tracer gas, and the sensitivity of the sensor and/or the detecting equipment for the actual tracer gas. In addition, the predetermined distance interval depends on which size of leaks that it is desired to detect. If it is desired to detect small leaks of a test object, the predetermined distance interval is shorter than if it is desired to detect larger leaks of the test object.
One way to avoid the risk of placing the sniffer tip and the spraying tip, respectively, at an incorrect distance from the leakage testing point is to perform a so-called global leak detection instead of a local leak detection. Both the sniffing method and the spraying method may be applied for global leak detection. In global leak detection, the test object is placed in a cabinet or test chamber, whereby it is tested whether the test object is leaking at any point or is leak tight, i.e. it is not tested whether there is a leak at a specific testing point, but the “total” leakage of the test object is tested. In case the sniffing method is utilized, the sniffer tip is positioned in the test chamber and any increase of the tracer gas concentration in the test chamber is detected. In case the spraying method is utilized, the spraying tip sprays tracer gas into the test chamber in order to surround the complete test object and any increase of the tracer gas concentration in the test object is detected. However, the global leak detection is not suitable to utilize for all types of test objects. More specifically, it is neither efficient nor cost effective when the test object is complex or has such dimensions that it is necessary to utilize a big or complex test chamber. Since many test objects have a complex design, local leak detection is commonly utilized.
One device which may be utilized in local leak detection and which comprises means for avoiding the risk of placing a sniffer tip at an incorrect distance from a test object is described in WO 2006/069877. More specifically, WO 2006/069877 describes a leak detector comprising a sniffer probe with a sniffer tip. The sniffer probe is provided with a distance detector for determining the distance between the sniffer tip and a test object. A leak detection test is only initiated if the distance between the sniffer tip and the test object corresponds to a predetermined value, whereby measurement errors due to placement of the sniffer tip at an incorrect distance from the test object are avoided. In a preferred embodiment, the distance detector is an optical detector, which comprises a light emitting device and a light receiving device. The light emitting device projects light onto a point on the test object and the light receiving device measures the intensity of the reflected light, whereby the distance between the sniffer tip and the test object is determined.
Thus, the leak detector described in WO 2006/069877 may be utilized to assure that the sniffer tip is positioned at a correct distance from the test object during a leak detection test. However, it may only be utilized to assure that the sniffer tip is positioned within a correct distance from the test object, not to assure that the sniffer tip is directed towards the correct testing point. This means that when the leak detector described in WO 2006/069877 is utilized, any point on the test object may be interpreted as the correct testing point if the distance between the point and the sniffer tip is correct. In other words, when utilizing the leak detector described in WO 2006/069877 the operator may direct the sniffer tip towards a point on the test object which is thought to be the correct testing point, but which is not. Then the leak test is performed at a correct distance from the test object, but at an erroneous point on the test object. The fact that an operator may direct the sniffer tip towards an erroneous point on the test object may be due to various facts. For example, many test objects are complex and many leakage test procedures are performed under poor lighting, whereby it may be difficult to see the intended testing point.
In view of the above, utilization of the leak detector described in WO 2006/069877 implies that the operator knows exactly where the leakage testing point is located on the test object and that the operator directs the sniffer tip towards that point. It is, thus, highly operator dependent, i.e. it is dependent on the behavior of the operator. In addition, the utilization of the leak detector described in WO 2006/069877 is also dependent on the properties of the surface of the test object.
Thus, there is still a need for a system for detection of a leak at a leakage testing point (i.e. which may be utilized for local leak detection), whereby the above mentioned drawbacks are avoided.